The present disclosure relates generally to medical fluid delivery and more particularly to dialysis fluid delivery.
Certain dialysis machines use electrically actuated solenoid valves to open and close fluid flow through associated tubing. Peritoneal dialysis (“PD”) is often performed at night while the patient is sleeping. It is accordingly desirable to minimize the acoustical noise that the dialysis machine generates, so as not to disturb the patient while sleeping. Moreover, it is generally desirable to produce equipment that is not noisy.
In many cases, the electrically actuated solenoid valves are of a normally closed type, in which the valves are spring or mechanically actuated closed (to occlude flow) and electrically actuated open (to allow flow). Such configuration provides a “fail safe” valve, which closes the tube, occluding fluid flow upon a loss of power. The spring pushes a plunger of the solenoid valve against the tube to occlude the tube, preventing flow. The spring closing of the valves does not cause significant noise because the valve plunger upon a release of electrical power is pushed against pliable tubing, which cushions the impact of the plunger, preventing significant noise.
Actuation or energizing of the valves, however, results in rapid acceleration of the plunger and a high velocity impact against a magnetic metal body of the solenoid. The impact generates a fairly significant amount of noise, which can wake the patient and be a nuisance generally. While solenoids can be configured to eliminate metal-to-metal contact, the elimination results in a significant increase in the power needed to hold the solenoid in the actuated position. Some solenoids are equipped with a permanent magnet that reduces the hold power to zero. These solenoids however require power to overcome the permanent magnet to close the plunger and tubing and therefore fail to meet the fail safe or power-fail-closed requirement.
A need therefore exists for a solenoid operated pinch valve for medical applications, which reduces actuation noise, without increasing the required hold power, and which operates in a fail safe or fail closed manner.